One concern for tire manufacturers is increasing the endurance of tires. Elastomers such as the rubber compositions commonly used in tires can age through oxidation, resulting in dramatic spatial variations in mechanical properties. These variations can cause a component to fail to meet design requirements or, in the worst case, to fail mechanically. Understanding oxidation involves characterization of chemical kinetics, species transport by diffusion, and the physical environment to which a rubber composition is exposed. These factors demonstrate the impact of component design on the oxidation process and are important for predicting a product's usable life.
It is beneficial to increase tire endurance by limiting oxidation of the tire's rubber composition. Because a substantial portion of the oxygen available to oxidize the rubber is supplied by the tire's inflation air, a known way of increasing tire endurance by reducing oxidation includes using a less permeable layer, such as a butyl rubber layer, against the inner walls of tires (see FIG. 1). Butyl rubber, however, is not completely oxygen-impermeable and therefore allows a limited amount of oxidation to occur throughout the tire and within critical areas of the tire.
Another known method for avoiding oxidation involves chemically trapping oxygen by accelerated thermo-oxidation of a rubber composition that acts as a buffer and is arranged between an oxygen source and a zone for which oxidation protection is desired. It is known to place such a composition between the inner face of the tire and the carcass ply to reduce the quantity of oxygen that comes into contact with the carcass ply from inflation air. Exposure to inflation air is a concern due to its high pressure. Using such a composition, however, has disadvantages including increased rolling resistance.
Another known method of reducing oxidation includes tire covers that protect the tire from atmospheric air. This method is obviously not practical for protecting tires in use and does not protect the tire from inflation air.
Typical tire construction, as shown in FIG. 1, is designed to meet various mechanical requirements depending on the specific application. However, consideration must also be given to how tire construction can impact durability, for which oxidation is a critical factor. The amount of oxygen transported through a tire is determined to a great extent by the butyl layer, or halobutyl inner liner, which essentially functions as an oxygen barrier due to its low oxygen diffusivity compared to the rubber composition that comprises the bulk of the tire.
An important component in the construction of tires is the wedge, which acts as an energy absorber. In a typical steel belted radial tire construction, the wedge rubber is inserted between two steel belt plies at an area of relatively high strain, usually toward the belt edges. The wedge rubber in a steel belted radial tire is added to help prevent belt edge separation (BES), which can increase tire durability. Other tire components affecting tire durability include, but are not limited to, the apex and the side wall.